Search for a shape isomer in $$^{233}$$Th

Abstract A search for a shape isomer in $$^{233}$$ 233 Th via delayed $$\gamma $$ γ decay was performed using the Heidelberg–Darmstadt Crystal Ball spectrometer together with a $$\varDelta E$$ Δ E – E telescope for light charged particle identification. Excited states in $$^{233}$$ 233 Th were populated through the $$^{232}$$ 232 Th( d , p ) reaction. The search for isomeric $$\gamma $$ γ decay was based on a total-energy reconstruction method: prompt energy deficits $$E_{\textrm{Miss}}$$ E Miss indicated possible long-lived isomeric states. Corresponding delayed summed energies $$E^{\textrm{Sum}}_{\textrm{del}}$$ E del Sum were recorded with the Crystal Ball. A two-dimensional analysis of $$E_{\textrm{Miss}}$$ E Miss versus $$E^{\textrm{Sum}}_{\textrm{del}}$$ E del Sum was carried out for various prompt and delayed multiplicities and for delayed time intervals up to 200 ns within the excitation-energy range $$E^{x} = 3$$ E x = 3 –7 MeV. No evidence of isomeric $$\gamma $$ γ decay was observed. The branching ratio for the population of a potential shape isomer in the second minimum of $$^{233}$$ 233 Th relative to the first minimum is constrained to $$ < 10^{-6}$$ < 10 - 6 , for isomeric states with energies $$E^{x} = 2$$ E x = 2